OBJECTIVES: 1) To discover the mechanisms of the decreased ability to recognize visual patterns in patients with syndromes of visual agnosia resulting from disease of the parietal occipital and temporal lobes of the brain. 2) To distinguish the visual disabilities of this group from those of patients with disease of the primary visual pathways. 3) By so doing to evolve a theory as to the important neuroanatomical connections for the functions of visual recognition and of visual localization in the human brain and to test a hypothesis already formulated as a result of preliminary studies, suggesting the dissociability of these two functions. METHODS: 1) Testing the effects of stimulus variables such as brightness, contrast, duration of stimulus exposure, stimulus size, and stimulus location on the ability to detect localize and recognize visual patterns in brain damaged patients, primarily victims of stroke. 2) Testing the effects of pattern masking on visual recognition on these patients. 3) Testing the strength of perceptual constancies (shape, size, brightness, color) in these patients. The analysis will relate patterns of disturbance in the above tests to the anatomic site of the lesion determined by CT scan, EEG, angiography, PEG, isotope scan and neuropathologic studies.